What happens when the physical body and the subjective sense of self part company? How do we explain phantom limbs and alien abduction? What are the cognitive, neurobiological mechanisms that support such phenomena? In this special issue of Cognitive Neuropsychiatry Spence and Halligan explore all these issues and more, with contributions drawn from an internationally renowned panel of authors. While some constrain the space of the body (as in neglect and dissociation syndromes), others seem to extend its boundaries (as with phantom limbs and autoscopy). Still others suggest a permeability of those boundaries (as in alien control and thought insertion, each occurring in schizophrenia). Finally, the body may itself be perceived as having passed into space (the most extreme exemplar being 'alien abduction').